Portable electronic devices such as laptop computers, cell phones, pagers, personal digital assistants, and the like are becoming more common in today's society as the capabilities and uses of such devices continues to expand. Many portable electronic devices are powered by a rechargeable battery, e.g., lithium, nickel-cadmium, or nickel-metal hydride type batteries, to facilitate the portable nature of such devices. Such portable electronic devices may also typically be powered by a DC power source when the situation permits, e.g., an AC/DC adapter plugged into a conventional AC outlet, which may also provide power to recharge the rechargeable battery.
Most portable electronic devices have an integral power supply block. The power supply block may contain a variety of circuits that provide a variety of power functions including coordination of power supply and delivery between a number of power sources, including enabling a battery to be recharged, without removing the battery from the portable electronic device.
As the efforts to extend operation time for portable electronic devices continues, some such devices may be equipped with two or more batteries. More sophisticated power supply blocks for use with an electronic device having two or more batteries may enable a user to use, remove, and/or insert any of the power sources, e.g., Battery A, Battery B, or an AC/DC adapter, without shutting down the portable electronic device.
A conventional power supply block that interfaces with two batteries and a DC power source may include anywhere between 12 to 16 switches, e.g., MOSFET transistors, and a large system capacitor, e.g., 100 pF, at the input to a DC/DC converter. Such a large number of switches and larger capacitor size increases price, uses valuable space on a PCB, slows down the high level integration of complex power supply blocks, and can decrease the mean time between failure (MTBF) which is a core measurement for portable electronic devices.
Accordingly, there is a need for a power supply block that overcomes the above deficiencies in the prior art by having less switches and a reduced system capacitor size.